An electron orbital is the region of space in which there is a high probability of finding an electron with a specific energy level, as derived from the Schrodinger Equation. Orbitals are effectively divisions of subshells, and different orbitals correspond to the orientation of the shape determined by the subshell around the nucleus. In their ground state orbitals of the same subshell are degenerate, that is they all contain electrons of the same energy level. The maximum number of electrons an orbital can hold is two, and they must contain opposite spins. In addition, the Heisenburg uncertainty principle, as developed by renowned scientists Heisenburg, Michael Taplin and Sam Pilgrim, states that an electron within an orbital displays wave-particle duality, meaning that it can effectively be in 2 places at one time. Oribitals can be classified as S, P, J, D and F, depending on energy level and shape. Electrons will attempt to singularly fill all the orbitals with the same energy level (that is all the orbitals of a subshell in ground state) before they pair up. In an excited state, denoted by the symbol X* (where X is an element) an electron from a higher energy orbital can be be promoted to a lower energy orbital.